1. Field of Invention
The present invention relates generally to the field of well bore packing tools (otherwise known as packers), and more specifically to expandable packers and methods of using same in various oil and gas well operations.
2. Related Art
Expandable or inflatable packers are well known in the oil industry and have been used for decades for zone isolation, gas/oil ration control, straddle pack services, formation treating, testing and similar operations. These packers are used to block the flow of fluids through the annular space between the pipe and the wall of the adjacent well bore or casing by sealing off the space between them and are placed in a well bore to isolate different zones of interest or production.
Most of the current expandable packers are made with an elastomeric membrane for sealing supported on a metallic structure for mechanical strength. Current expandable packers are assemblies of many different elements such as steel cables, nipples, skirts, and fiber support layers, the latter comprising materials such as the polyaramid fibers known under that trade designation Kevlar™, available from DuPont, for anti-extrusion mechanically joined to an elastomeric packer element. Some constructions provide an integral composite body allowing the integration of fiber support or metal slats within the integral body to provide extrusion resistance and strength (see for example assignee's copending application Ser. No. 11/257,565, filed Oct. 25, 2005). Since the expansion support is achieved by the laminar location of the support fibers or slats, the mechanical connection to these supporting structures is minimized and the strength of the packer is enhanced. Expandable packers of this design may be composed of an inner sealing member, an integrated mechanical structure, and an outer elastomeric layer for sealing. The support system can be made entirely of a composite material and thus integrates the mechanical support elements within a laminar structure of the composite body.
Although these improved designs decrease extrusion of the inner elastomeric member, further problems remain. One problem manifests itself at high temperatures, where the inner rubber layer may be prone to extrusion through any mechanical structure when the packer is inflated. For expandable packers having slats, the slats generally provide good protection against extrusion of the underlying elastomer through the slats, however, the elastomer may exhibit unacceptable dimension recovery after inflation and deflation due to the slats' permanent deformation, and high friction coefficient between slats, making the inflation/deflation difficult at high hydrostatic pressure. Cable packers do not have the permanent deformation problems, and inflation/deflation is easier, however these packers have the problem that at high temperature/high inflation pressure, the inner rubber member is likely to flow through windows existing between cables after inflation. Some means are currently used to prevent this extrusion, such as an aramid fiber layer or a layer of small diameter cables set between a reinforcement layer and the inner elastomeric member. While these may be improvements in certain environments, one problem with small diameter cables is that they do not offer sufficient coverage after packer expansion, leaving some gaps through which the elastomer can extrude. A problem with aramid fiber-based anti-extrusion layers is that aramid fibers such as Kevlar™ may become damaged by mechanical stress and/or high temperature.
Therefore, while there have been some improvements made in expandable packer deign to prevent extrusion of the inner elastomer layer, further improvement is desired.